Appendix A, which is part of the present disclosure, is a microfiche appendix consisting of one (1) sheet of microfiche having 13 frames. Microfiche Appendix A includes a software program, in accordance with the present invention, operable on a host processor.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
This and other embodiments are further described below.
The present invention relates to personal verification systems which utilize sensors to obtain biometric information from a user. More particularly, the present invention relates to a method of imaging fingerprints that are difficult to image and of concealing latent prints left behind on the sensor.
Personal verification systems utilize a variety of systems and methods to protect information and property and to authenticate authorized users. Some protection systems rely on information acquired by biometric sensors relating to the biometric features of a user""s body. The use of biometric information for authentication is advantageous, because each biometric feature is unique to the user. Any biometric feature can be used, including facial features, a retinal image, palm print, fingerprint, or signature. Where the biometric feature is a fingerprint, the biometric sensor obtains information representative of the user""s fingerprint.
One disadvantage of biometric sensors is background noise. Background noise caused, for example, by nonuniformity among the transistors of a sensor or environmental conditions, such as dirt, interferes with the signal produced by the sensor, making it difficult to produce a clear image or representation of the biometric feature. Background noise can be problematic for capacitive sensors as well as for sensors which detect speech. For example, for a capacitive sensor that images fingerprints, the background noise generated by the sensor makes it difficult to accurately image very dry fingers. A dry finger placed on the sensor produces a weak signal that can be obscured by the background noise of the sensor. As a result, it may be difficult to determine the unique minutiae from the resulting image or representation of the fingerprint, thereby hampering either the identification or authentication process.
Another problem with biometric sensors, particularly ones in which the user places a body part directly on the sensor, is the remnant of a latent print. For example, natural oil from the user""s hand will leave a residue of a fingerprint or palm print on the sensor. Under the right condition, the sensor can be made to read the latent print as if there was an actual finger on the device, and the user could obtain unauthorized access to the protected system.
There is a need, therefore, for a method of eliminating background noise so as to improve the image or representation produced by a biometric sensor. In addition, because the method of eliminating background noise can also make latent prints much more visible, there is also a need for a method of preventing latent prints from being used to gain access to a protected system.
In accordance with an embodiment of the invention, a method is provided for operating a personal verification system. The method includes acquiring with a sensor a first image of a first biometric feature and storing at least a portion of the first image. The method further includes acquiring with the sensor a second image of a second biometric feature, comparing at least a portion of the second image to the first image, and displaying the second image if the second image is substantially different from the first image. The portion of the second image that is compared to the first image is the same portion as the stored portion of the first image.
In accordance with another embodiment of the invention, a method of operating a personal verification system includes measuring or estimating a background noise from a biometric sensor and acquiring a first image of a first biometric feature positioned on the sensor. The background noise is then removed from the first image to obtain a noise-reduced image. The method further includes applying a gain to the noise-reduced image to enhance it further.
In accordance with still another embodiment of the invention, a method is provided for operating a personal verification system. The method includes generating a first image of a first biometric feature positioned on a sensor and storing at least a portion of the first image before or when the first biometric feature is removed from the sensor. The method also includes generating a second image of a second biometric feature positioned on the sensor and comparing at least a portion of the second image to the first image. Both the first and second images can be noise-reduced images. The method further includes displaying the second image only if the second image is substantially different from the first image.
Thus, the present invention provides a couple of benefits and advantages. The present invention provides an improved image of a biometric feature, by eliminating or reducing background noise, thereby making it possible to image dry fingers. In addition, the present invention conceals latent prints to prevent unauthorized persons from accessing the system. By comparing a newly acquired image of a biometric feature with the most recent prior image and displaying the newly acquired image only if the two are different, the system ensures that the user is not using a latent print to access the system.